Process of tempering metal



No. 6l4,928. Patented Nov. 29, I898.

G. D. BURTON.

PROCESS OF TEMPERING METAL.

(Application filed Mar. 13, 1897.]

2 Sheets-Sheet l.

(No Model.)

Patented Nov. 29, I898. G. D. BURTON. PROCESS'OF TEMPERING METAL. \Applicntion filed Mar. 13. 1897.)

2 Sheets-Sheet 2.

No. 6l4.928.

(In Modal.)

UNITED STATES PATENT OEEIcE.

GEORGE D. BURTON, OF BOSTON, MASSACHUSETTS.

PROCESS OF TEMPERING METAL.

SPECIFICATION forming part of Letters Patent No. 614,928, dated November 29, 1898. Application filed March 13, 1897. Serial No. 827,420. (No specimens.)

T0 aZZ whom it may concern.-

Be it known that I, GEORGE DEXTER BUR- TON, a citizen of the United States of America, residing at Boston, in the county of Suffolk, in the State of Massachusetts, have invented certain new and useful Improvements in the Art of Tempering Metal by the Electroliquid Process, of which the following is a specification.

This invention relates to the heating and cooling of metals for the purpose of hardening or softening them.

The objects of the invention are to avoid oxidation and scales on the surface of the metal and to facilitate the operation.

The invention consists in the art of tempering metal by subjecting it to the action of an electric are formed between it and an electrolytic bath until the proper heat is obtained, then cutting off the current and permitting the article to be cooled in said bath, the heating and cooling operations being performed without removing the article from the bath.

Figure 1 of the, accompanying drawings represents a perspective view of an apparatus for carrying out this process. Fig. 2 represents a longitudinal vertical section thereof. Fig. 3 represents in part an end elevation and in part a transverse section of a box disposed at one end of the electrolytic tank or vessel constituting a part of this apparatus. Fig. 4 represents, on an enlarged scale, a transverse section of the vertically-adjustable bar electrode adapted to be inclosed in said bar and the means for holding it in elevated position.

Similar numerals indicate corresponding parts in all the figures.

Any suitable apparatus may be employed for carrying out this process. The apparatus herein illustrated comprises a vessel for containing an electrolytic solution 20. This vessel, preferably in the form of a tank, is constructed of or lined with material which is a non-conductor of electricity.

An electrolytic bath is disposed in the tank 10 and partially fills said tank. This bath consists of any suitable electrolytic solution, being one which will cause, with the electric current under proper conditions, the formation of a voltaic are between the metal to be heated and tempered and the liquid. The electrolyte should be of a specific gravity greater than that of Water, and it may consist of an acid or an alkaline watery solution, preferably the latter.

The chemical ingredients added to the water produce the necessary density in the bath to cause the heating action to take place, increasing the conductivity thereof and facilitating or enabling an arc to be formed between the metal and the liquid. A density of at least 1.025 to 1.105 should be used. WVhen it is desired to harden the metal to a considerable degree, the bath should be of a greater den sity, and consequently of a higher conductivity, say 1.200 to 1.250.

For hardening steel or iron a bath of chlorid of sodium and sulfuric acid may be employed. I have used for this purpose a bath composed of seventy-two gallons of water, three gallons of sulfuric acid, and fifty pounds of chlorid of sodium or rock-salt.

For annealing or softening iron or steel I have used a solution composed of a barrel of water, five pounds of borax, and five pounds of sal-ammoniac. This bath will answer also for the softer metals, such as brass or copper and compositions of these metals.

An anode-plate is disposed in the tank and has a contact-surface with the solution much greater than the area of contact of the article to be heated. This plate is composed of lead, carbon, or other suitable conductive material and is disposed at any convenient point in the tank. As shown, it is disposed transversely of the tank, at one end thereof, and is preferably provided with a fixed rod 31, which extends up above the top of the tank. The anode-plate is preferably protected by a screen 85, composed of non-conductive material and so constructed as to permit the passage of the liquid to the anodeplate.

A conductor 40 connects the anode-plate with the positive pole of an electric source.

An upright cylinder is supported in a socket in the bottom of the tank. This cylinder is composed of an outer tube 51 of Wood or other material and an inner tube 52 of asbestos, wood, rubber, or other insulating material.

A plunger 60, composed of wood or other non-conducting material and provided with a longitudinal groove 61 and a metallic conductive cap 62, is adapted to play up and down in the cylinder 50. A dependent bracket 63 is connected with the cap at the upper end of the plunger. This bracket is composed of two arms having outturned flanges 64 and 65 at their lower ends, to which a work-holder is attached. These flanges have studs 66 and 67.

The work-holder may consist of any suitable means for holding the work or article to be softened or hardened in the solution. In the form shown it comprises a non-conducting plate 70, attached to the bracket 63 of the plunger 60. This plate has a hole 71 in the center larger in diameter than the cylinder 50, through which said cylinder extends. Two clamping-jaws 72 and 73 are adapted to slide in cleats 76 and 77 011 the upper face of the plate 70. These clamping-jaws are provided at their front ends with lips which depend over one edge of the plate and at their rear ends with studs 7 1 and 75. Springs 78 and 79 connect the studs 76 and 77 on the jaws with the studs 66 and 67 of the bracket 63. These springs serve to draw back the jaws, so as to cause them to clamp the work against the edge of the plate 70 and they also serve as electric conductors for the passage of the electric current. These clamping-jaws are connected by a handle whereby they may be drawn out for releasing or inserting the work. with the movement of the plunger to depress the work below the surface of the solution in the tank and to withdraw it from said solution.

The means for raising and lowering the plunger, and consequently the work-holder, may consist of a foot-lever 80 or a hand-lever for lowering the plunger and a spring 86 for raising it.

A conductor is connected at its inner end to the metallic cap 62 on the plunger 60 and lies in the groove 61 thereof.

A switch is preferably disposed on one side of the tank 10 and provided with two contacts 111 and 112 and a switch-leverl13. The outer end of the conductor 100 is connected with the contact 111, and the contact 112 is connected with a branch 121 of the main conductor 120, leading to the negative pole of the electric source.

In the use of this process for tempering a saw, for instance, the saw is clamped between the edge of the plate 70 and the sliding jaws 72 and 73 and the work-holder is depressed by the foot or hand lever, so as to project the portion of the saw to be heated and tempered below the surface of the liquid. The switch-lever being in operative position, the current passes from the anode plate through the solution to the work and an arc is formed between the work and the solution, the current passing to the negative pole through the clamping-jaws 72 and 73, studs 76 and 75, springs 78 and 79, bracket 63, cap 62, and conductor 100, switch 110, and con- The plate 70 moves up and downductor 120. The work remains in this position with the current on until the portion thereof to be tempered is sufliciently heated by the arc, and then the switch 110 is operated to break the circuit. The are then disappears and the solution il'nmediately comes in contact with that part of the work which has been heated by the arc. The work is held in this position and is cooled by the action of the liquid in the same liquidin which it was heated. Vhen sufficiently cooled, the leveris released by the operation of the spring, causing the work-holder to lift the work out of contact with the solution. then taken from the work-holder and another article placed therein and the operation repeated.

By this process and apparatus the particular parts of the article to be hardened or softened-as, for instance, the edge of a saw-- may be heated and cooled in the bath without exposure to the action of the air, and the body of the article may remain cool or practically unheated and unchanged in character. In this way the body of the tool, such as a saw, is not necessarily hardened, as is sometimes the case where the blade is heated in the old way, where it is heated throughout its body. In that case it becomes brittle and more liable to break, whereas in this case the body or back of the saw-blade remains comparatively soft and is not liable to break. Moreover, there is no oxidation of the edge of the saw by this method, and consequently there is no loss of the metal caused by oxida tion.

At one end of the tank is disposed a conductor adapted for use in heating articles in the bath by resting their bodies in contact with said conductor. This conductor is in the form of a hinged bar 150, disposed in a box 160, having a lid 161, so that it may be closed and protected when not in use. The support for the bar comprises a yoke-shaped device 17 O, which is preferably movable in the box, having upright lugs at opposite ends of its connecting-bar, and the conducting-bar has trunnions whereby it is pivoted on these lugs 171 and 172. The outer wall of the box has a slot 162 and the yoke has a stud 17 3, which projects through said slot. In Fig. l the box is shown as closed, and also in Fig. 3 in full lines the box is shown as closed. \Vhen it is desired to utilize the bar 150 for heating metals, the lid of the box is opened and the stud 173 is raised and held by any suitable catch device. The catch device herein shown comprises vertical racks 176 and 17 7 disposed on the front of the box 160, and a latch 17S, pivoted to the stud 173 and adapted to 011- gage the rack, as clearly shown in Fig. 1. The lifting of this stud raises the yoke 170, and consequently the bar 150, and the latter is swung over the edge of the tank, as indicated in dotted lines in Fig. 3. In this position it is adapted to serve as a conductive rest for any metal articles to be projected into the The work is liquid. The bar is connected with the negative source by the wire 180, which is connected with the main negative wire 120. This wire plays in the slot 164 in one end of the box.

I claim as my invention- 1. The process of tempering metal which consists in subjecting it to the action of an electric arc sprung between it and an electrolytic bath, until the proper heat is obtained, then cutting off the current and permitting the article to cool in said bath, both the heating and cooling operations being performed without removing the metal from the bath.

2. The process of tempering metal which consists in immersing or partially immersing it in an electrolytic bath, forming an electric are between said metal and said bath until the metal is heated to the required temperature, then shutting oif the current and per mitting the article to remain in the bath until cool, whereby oxidation is prevented.

3. The art of hardening a-portion of a metal tool which consists in immersing the portion to be hardened in an electrolytic bath and passing an electric current through said bath and tool forming an electric are between the bath and the portion to be tempered until such portion is heated to the proper degree, then cutting off the current and permitting the heated edge to cool in said bath, the portion of the tool above the surface of the liquid remaining practically unheated, and un changed.

GEO. D. BURTON. 

